Heretofore, engines for self-propelled road vehicles have been predominately Otto or Diesel cycle. The predominant fuels have been gasoline and diesel fuel, both produced from petroleum, thereby depleting a non-renewable source. The resultant exhaust emissions degrade environmental quality, damaging health and economic activity, both public and private
One approach to amelioration of these depletions and degradations is the use of alternate fuels such as alcohol, propane, methane and hydrogen.
The disadvantages of each alternative fuel can be evaluated in terms of:
1. renewability PA1 2. effect on environmental quality in the short term (smog) PA1 3. effect on environmental quality in the long term (greenhouse). PA1 1. non-working volume is larger; PA1 2. apex seal leaning angle is larger; PA1 3. more apex and side seals are needed; PA1 4. more apex/side seal joints are needed; PA1 5. inlet and exhaust ports are adjacent, increasing heat exchange between them and thereby decreasing efficiency. PA1 is simpler and more efficient, PA1 is self-starting, PA1 needs no warm up period, PA1 uses the best of the alternate fuels and PA1 improves environmental quality. PA1 1. non-working volume is smaller; PA1 2. apex seal leaning angle is smaller; PA1 3. fewer apex and side seals are needed; PA1 4. fewer apex/side seal joints are needed; PA1 5. inlet and exhaust ports are not adjacent, decreasing heat exchange between them and thereby increasing efficiency.
One of the disadvantages of propane fuel is that it is not easily renewable; however, renewability is feasible for alcohol and methane through photosynthesis and for hydrogen through solar driven hydrolysis of water.
One of the disadvantages of alcohol fuel combustion is production of aldehydes, highly oxidizing components of smog.
The relative disadvantage of each alternate fuel as it contributes to the greenhouse effect can be estimated in terms of the relative amount of carbon dioxide per unit of thermal energy available for complete combustion. Gasoline, diesel and alcohol fuels all produce about the same amount of carbon dioxide per thermal energy unit, propane produced about 94% of that amount, methane about 80% and hydrogen none at all.
Whichever fuel is used, the fact that the Otto and Diesel cycle engines are not self-starting has resulted in the disadvantage that, according to the South Coast Air Quality Management District in El Monte, California, as reported by Science News of Feb. 10, 1990, vehicles idling in traffic burn one-quarter of all fuel sold in Los Angeles, Orange, Riverside and San Bernardino counties.
A self-starting engine is defined here as an engine that produced torque immediately upon demand from zero shaft speed at any shaft position. If an engine must be equipped with what is called a self-starter, it clearly cannot be a self-starting engine. Otto and Diesel cycle engines cannot be self-starting. In contrast, some reciprocating piston steam engine can be self-starting as long as steam pressure is available. Heat engines that can be self-starting such as steam engines, Rankine cycle engines in general and Stirling cycle engines do need time to warm up before they can be self-starting and require some power input to maintain the warmed up state that enables self-starting.
Other heat engines such as turbines and Joule cycle engines in general are not self-starting.
Electronic motors can be self-starting without a warm up period, but electric engines have the disadvantage that an expensive, heavy electric storage battery which limited life is required for a self-propelled vehicle.
A general disadvantage of the use of air as the oxidizer in heat engines is that the higher cycle temperature necessary to increase thermodynamic efficiency also increases production of nitrogen, dioxide, a major component of smog.
The disadvantages of rotary piston machines with three side pistons relative to those with two sided pistons are: